Abstract: To investigate the effect of outgassing from a certain material on holding vacuum degree in a minisized container (10^-5 m³), a special testing system was developed with the pressure rise method used. The Kovar alloy with passivated surface was taken as sample and its outgassing rate under given conditions was tested. The results showed that the surface outgassing rate per unit area is in the range from 5.1 × 10^-13 to 2.1 × 10^-13 Pa·m³·s^-1·cm^-2 in first 10 hr after baking at 150°C for 2 hr, and the total outgassing throughput per unit surface area is about 2.6 × 10^-8 Pa·m³·cm^-2 for 40 hr. The outgassing composition consists of H₂, H₂O, N₂ and/or CO, as shown in the spectra by quadrupole mass spectrometry. A mathematic model was developed to describe how the process of surface outgassing affects the vacuum degree in a minisized container with the pressure boost formula calculated. The key influencing factors on the normal performance and service life of the minisized container were investigated to find them so as to improve the method proposed.